A UPS is an abbreviation of Uninterruptible Power Supply, and as a power device that normally keeps a battery in a fully charged state by receiving the commercial power or the generator power and when the power is lost, discharges the battery in order to continuously supply electricity to the load for a predetermined time without momentary power failure, is a device that always supplies the rated voltage and the rated frequency electricity to the load even if the voltage fluctuation and frequency fluctuation of the input power occur.
Batteries are used in such UPS devices, and since batteries used in UPS devices supply power to electronic devices when main power supplied to the electronic devices is interrupted, they remain fully charged for most of the time.
In a typical BMS, a battery fully charged state is determined based on the output voltage and current of a battery and the holding time of the output voltage and the current.
FIG. 1 is a graph illustrating an output voltage according to the charging capacity of a battery.
Referring to FIG. 1, it may be seen that the output voltage of the battery increases as the charging capacity increases.
On the other hand, even with the same battery, the charging capacity changes due to a chemical change inside the battery depending on a temperature.
Table 1 shows the charging and discharging capacity of a battery according to a temperature under the same conditions.
TABLE 1CHARGINGTEMPERATUREDISCHARGING TEMPERATURE (° C.)(° C.)−100254560−5100%113%———10120%115%130%——25104%117%134%139%139%45——135%140%140%60———141%141%
In the above table, when charging and discharging are performed at a high temperature, a charging capacity of more than 40% remains as compared with a low temperature.
In the case where the charging capacity of a battery remains, power may be supplied using the battery for a longer time than the specification but in the case where the battery maintains a full charge state, the charging capacity of the battery is exceeded, so that this shortens the lifetime of the battery.